1. Field of the Invention
This invention relates to the field of guidance systems, and more particularly concerns a beamrider guidance system with feedback.
2. Description of Related Art
Beamrider guidance systems are often used in missile systems to guide a missile to a target. Such systems often use a beam which is projected onto the target by a projector or in a lead angle direction with respect to the target. The beam is initially referenced to the target by the operator which views the target through a boresight. Because the boresight is often mechanically or electrically linked to the projector, movement of the boresight causes a similar movement in the projector and therefore the beam. Once the target is located through the boresight, the missile is launched and follows the beam to the target.
During flight, the beam is received by a detector on the missile and is used by the missile electronics to determine whether the flight path of the missile should be corrected. Such a determination is possible since the beam is generally spatially encoded. If the missile strays outside the center of the beam, the detector senses the signal encoded in the beam which indicates the missile's relative position with respect to the center of the beam. The detector then delivers an appropriate signal to the autopilot of the missile to cause the autopilot to adjust the flight path of the missile. In this manner, the missile is able to correct for variations in its flight path while following the beam to the target.
To ensure that the beam is focused with respect to the target when the target was sighted through the boresight, the geometric relationship between the boresight and the projector optical axis, in particular the center of the coded beam cross-section, had to be accurately calibrated. If the position of the boresight with respect to the projector reference coordinate system was not so calibrated, sighting the target through the boresight would not always cause the beam to be directed on or referenced to the target. Further, once the boresight was calibrated with the projector optical axis and the center of the coded field during assembly, the calibration could not easily be maintained as the launcher containing the boresight and the projector was often jarred during use. In addition, the detector on the missile which received the beam often had errors caused by biases and offset unbalances which degraded overall guidance performance. Finally, the initial calibration was often difficult to achieve as the boresight, the projector optical axis and the far field coding center often do not lend themselves to production oriented, repeatable tests and calibration procedures. In addition, and the projector often did not have the same optical center as the boresight.